Decorative laminates are well known articles of commerce which have been produced for many years, finding extensive use as table tops and wall surfaces. Normally, the surface has a high gloss or satin finish. In some cases, however, it is desirable to have a semi-dull, rough or embossed finish.
To impart this rough or embossed finish to a laminate surface by means of an embossed pressing plate would be very expensive. Embossed finishes have been impressed by using a perforated stencel or solid embossed metal sheet, as an embossing sheet in a laminate assembly, as taught by Grosheim in U.S. Pat. No. 3,418,189 and Olsen in U.S. Pat. No. 2,070,023. This type of embossing sheet, however, has a tendency to rupture the protective overlay and print sheets in the laminate assembly, ruining the finish, and allowing resin from the core of the laminate assembly to bleed through to the laminate surface.
Hunt, in U.S. Pat. No. 2,861,372, recognized these problems. He used a wire screen sandwiched between two aluminum foils as a texturing sheet assembly, in a thermoplastic resin impregnated laminate stack up, using pressures of about 200 psi for laminate bonding. This provided a soft, lightly textured effect on the laminate surface, the aluminum absorbing most of the texturing effect from the screen. Hunt stitched, stapled or roll pressed the aluminum foil edges to seal in the screen. He required that the texturing assembly be of larger area than the laminate stack up, so that the seal would not mar the laminate finish.
Such an embossing assembly produces problems on a modern production line, where Hunt's sealing procedure would be difficult to use with large laminates, and where all elements in the laminate stack up are generally required to be the same area size. Also, for bonding of thermoset resin impregnated laminates, where pressures of 800 psi to 1500 psi are required, the wire screen would generally cut through the exterior aluminum foil sheets, unless the foil was very thick with resultant poor texturing effect. Such use of aluminum foil also tends to produce soft texturing rather than the sharp embossing or patterning which is highly desirable.
What is needed then, is a commercially useful type embossing assembly, that will impart a sharp embossing or other type decoration to thermoset high pressure laminates without cutting or otherwise marring the laminate surface.